The oceanic manta rays, Mobula birostris, filter big volumes of water while feeding on zooplankton. Thus, they are potentially exposed to the growing threat of plastic pollution. Ingested plastics can leach adsorbed toxic pollutants and plastic additives (e.g. phthalates, used as indicators of plastic contamination in animal tissues) that are recognized as endocrine disruptors and toxic for many species. The oceanic manta ray populations of the Gulf of California have been drastically reduced in recent decades, making the Revillagigedo Archipelago and Banderas Bay its last refuge and aggregation areas in the Mexican Pacific Ocean. Samples have been collected from the sea surface using a manta net: floating plastics were found in both areas, we determined the size and polymer composition of the plastic debris through Fourier transform infrared spectroscopy (FT-IR). Small tissue samples (skin and muscle biopsies) of manta rays have been collected during scuba and freediving using a spear pole and will undergo chemical extraction and subsequent analysis to measure the concentration of phthalates. Chemical analysis of these plastics collected in the area has been carried on to quantify polychlorinated biphenyls, pesticides and polycyclic aromatic hydrocarbons that were adsorbed on the surface of plastic debris. Measuring phthalates in manta ray biopsies is a valid non-lethal method to investigate possible plastic ingestion occurrence in this species, that is considered vulnerable to extinction by IUCN and protected in Mexico. This research is a baseline study for plastic debris contamination in the area and for possible ingestion by oceanic manta rays.